Branch polybenzazole polymer and method of preparation

ABSTRACT

The invention is a process for making novel branched polybenzazole polymers and the polymers formed thereby. Novel compounds are also disclosed that are useful as branching agents in making the branched polybenzazole polymers. The branched polymers synthesized by the process can be formed into strong, light articles such as fibers and films.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with support of the United States Governmentunder Contract F33615-85-C-5113 awarded by the Department of the AirForce. The Government has certain rights to this invention.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of copending application Ser. No.07/401,346 filed Aug. 31, 1989, now U.S. Pat. No. 5,124,432.

BACKGROUND OF THE INVENTION

The present invention concerns the art of PBZ polymers and in particularbranched compositions containing those polymers.

PBZ polymers (see definition for PBZ polymers herein) are commonly knownas polybenzoxazoles, polybenzothiazoles and polybenzimidazoles. PBZpolymers and their synthesis are described in detail in the followingpatents and article, the teachings of which are incorporated herein byreference: Wolfe et al., Liquid Crystalline Polymer Compositions,Process and Products, U.S. Pat. No. 4,703,103 (Oct. 27, 1987); Wolfe etal., Liquid Crystalline Polymer Compositions, Process and Products, U.S.Pat. No. 4,533,692 (Aug. 6, 1985); Wolfe et al., Liquid CrystallinePoly(2,6- Benzothiazole) Compositions Process and Products, U.S. Pat.No. 4,533,724 (Aug. 6, 1985); Wolfe et al., Liquid Crystalline PolymerCompositions, Process and Products, U.S. Pat. No. 4,533,693 (Aug. 6,1985); Evers, Thermooxidatively Stable Articulated P-Benzobisoxazole andP-Benzobisthiazole Polymers, U.S. Pat. No. 4,359,567 (Nov. 16, 1982);Tsai et al., Method for Making Heterocyclic Block Copolymers, U.S. Pat.No. 4,578,432 (Mar. 25, 1986); and "Polybenzothiazoles andPolybenzoxazoles", 11 Ency. Poly. Sci. & Eng., 601-635 (J. Wiley & Sons,Inc. 1988).

PBZ polymers have generated considerable research interest due to theirunique physical properties. PBZ polymers can exhibit remarkablehigh-temperature stability, high tensile strength and high tensilemodulus. PBZ polymers are resistant to harsh environments and,therefore, useful for military, aerospace, automotive, and otherapplications requiring high performance materials.

Due to their unique thermal and environmental stability, PBZ polymerscan be difficult to fabricate into useful articles of manufacture,especially where the PBZ polymer is a rigid-rod PBZ polymer, Rigid-rodPBZ polymers are those polymers which consist of essentially rectilinearpolymer structures. In general, useful articles are made from bothrigid-rid and non-rigid-rod PBZ polymers by dissolving them in asuitable solvent, typically polyphosphoric acid, to form eitheranisotropic liquid crystalline compositions or isotropic compositions,the nature of the resulting composition depending upon the PBZ polymerin question and its concentration. These compositions can be processedby known methods to form fibers and films. The fibers can beincorporated as a reinforcing agent within a thermosetting polymer, suchas an epoxy resin, to form a composite that can be converted intostrong, light articles of manufacture.

SUMMARY OF THE INVENTION

One aspect of the present invention is a process for making branched PBZpolymers. The process comprises contacting, in the presence of at leastone dehydrating solvent and under conditions sufficient to form abranched PBZ polymer, at least one PBZ monomer with at least onebranching agent. The PBZ monomer(s) and the branching agent(s) arepresent in amounts sufficient to form a branched PBZ polymer. Each PBZmonomer contains at least two azole-forming moieties and is capable offorming a PBZ polymer in a condensation polymerization reaction. Eachbranching agent comprises a base structure moiety which has bondedthereto at least three moieties, each of which, when reacted with anazole-forming moiety from a PBZ monomer, forms an azole ring, thebranching agent being present in an amount which will produce a branchedPBZ polymer substantially free of cross-linking.

A second aspect of the present invention is a branched PBZ polymer. Thebranched PBZ polymers comprise at least one branching agent basestructure moiety having a plurality of PBZ polymer branches bondedthereto.

A third aspect of the present invention is a group of branching agentsuseful in making branched PBZ polymers. The branching agents arecompounds selected from the group consisting of: ##STR1## wherein: Ar¹is a first aromatic group;

Ar² is a second aromatic group;

P¹⁻⁴ are independently selected from the group consisting ofelectron-deficient carbon groups and o-amino-basic moieties; and

Z, Z¹ and Z² are independently selected from the group consisting of isO, S or NR, R being hydrogen, an aliphatic group containing up to about12 carbon atoms or an aromatic group containing up to about 18 carbonatoms.

A fourth aspect of the present invention is a dope comprising at leastone solvent and at least one branched PBZ polymer.

A fifth aspect of the present invention is an article of manufacturecomprising at least one branched PBZ polymer.

DETAILED DESCRIPTION OF THE INVENTION I. Definitions

The following terms are used repeatedly in this application and have themeanings and preferred embodiments set out in the correspondingdefinitions, unless otherwise specified.

Aromatic group (Ar)--An aromatic group is an aromatic ring or ringsystem as defined herein. The size of the aromatic group is notcritical, so long as the aromatic group does not significantly hinderreaction of the moiety in which it is incorporated. Each aromatic groupsuitably comprises no more than about 18 carbon atoms, preferably nomore than about 12 carbon atoms and most preferably no more than about 6carbon atoms. Each aromatic group may be heterocyclic, but is preferablycarbocyclic and more preferably hydrocarbyl. If the aromatic group isheterocyclic, the heteroatom is preferably nitrogen.

Unless otherwise specified, an aromatic group broadly refers to arenes,a major group of unsaturated cyclic hydrocarbons containing one or morerings, which may comprise a single aromatic ring, a fused ring system oran unfused ring system containing a plurality of aromatic rings. Wheretwo or more rings are present, they may be fused, as in the case ofpolynuclear compounds such as naphthalene and anthracene, or covalentlybonded to each other either directly, as in the case of a biphenylmoiety, or by way of an intermediate moiety. Suitable intermediatemoieties comprise, for example, a carbonyl group, a sulfonyl group, anoxygen atom, a sulfur atom, an alkyl group, an aromatic group, orcombinations thereof. Each aromatic group is preferably a single6-membered ring, and most preferably a benzene ring.

Aromatic groups are generally inert with respect to the condensationpolymerization reaction. Each aromatic group may have substituentsattached thereto which are stable with respect to reactants and solventsused in PBZ polymerization reactions and do not interfere withreactivity of azole-forming moieites attached to the aromatic group.Examples of suitable substituents include hydrogen, halogens, alkoxymoities, aryloxy moieties and alkyl groups. Substituents are preferablyhydrogen, alkyl groups having no more than about 6 carbon atoms, andhalogens.

Azole ring--An oxazole, thiazole or imidazole ring as illustrated inFormula 1. The carbon atom bonded to both the nitrogen atom and the Zmoiety is the 2-carbon. The Z moiety is O, S, or NR, R being selectedfrom the group consisting of hydrogen, aromatic groups containing up toabout 18 carbon atoms, and aliphatic groups containing up to about 12carbon atoms. R is preferably hydrogen or an alkyl group, and mostpreferably is hydrogen. Where R is an alkyl group, it suitably comprisesno more than about 6 carbon atoms, preferably no more than about 4carbon atoms and most preferably no more than 1 carbon atom. Each azolering is preferably an oxazole ring or thiazole ring, and more preferablyan oxazole ring. In PBZ polymers, the 4- and 5-carbons of each azolering are typically fused with an aromatic group, as shown in Formula 1.##STR2##

Azole-forming moiety--An "o-amino-basic moiety" or "electron-deficientcarbon group" as those terms are defined herein. An azole ring is formedby the reaction of an electron-deficient carbon group and ano-amino-basic moiety. Branching agent--A reactant, defined in greaterdetail hereinafter, which can react with at least one PBZ monomer in adehydrating solvent to form branched PBZ polymers.

Dehydrating Solvent--Any non-oxidizing liquid solvent capable of placingat least a portion of the branching agents, PBZ monomers and resultingbranched PBZ polymer into solution during a PBZ polymerization reaction.The dehydrating solvent must not substantially oxidize reactantsdissolved therein which contain o-amino-basic moieties. The dehydratingsolvent must also compensate for water formed during the polymerizationresulting from an azole ring forming reaction between anelectron-deficient carbon group and an o-amino-basic moiety. It is alsobelieved that dehydrating solvents facilitate azole ring formation.Examples of suitable dehydrating solvents include strong mineral acidssuch as sulfuric acid, methanesulfonic acid with added phosphorouspentoxide (P₂ O₅), trifluoromethyl sulfonic acid, polyphosphoric acidand mixtures thereof.

The dehydrating solvent is preferably polyphosphoric acid or a mixtureof methanesulfonic acid with added P₂ O₅. The polyphosphoric acidsuitably has a minimum P₂ O₅ content of at least about 73% by weight ofsolution, and desirably at least about 75%. The maximum P₂ O₅ content isdesirably less than about 90% and preferably is less than about 86% byweight of solution. The weight ratio of methanesulfonic acid to P₂ O₅ inmixtures containing those compounds is preferably no more than about20:1. Those persons skilled in the art recognize that the actual P₂ O₅content in methanesulfonic acid will vary depending upon the PBZ monomeremployed and desired end use for the resulting polymer. In general,mixtures containing a ratio of methanesulfonic acid to P₂ O₅ of greaterthan about 5:1 are used to obtain isotropic solutions, while ratios lessthan 5:1 are typically used to obtain anisotropic solutions.

Electron-deficient carbon group (Q)--Any group containing anelectron-deficient carbon atom which can react in a suitable dehydratingsolvent with an o-amino-basic moiety to form an azole ring. Acceptablegroups representative of electron-deficient carbon groups are thoselisted in column 24, lines 59-66 of U.S. Pat. No. 4,533,693, theteachings of which are incorporated herein by reference. Preferredelectron-deficient carbon groups are carboxyls, acyl halides, acylesters, acyl amides, anhydrides, alkali or alkaline earth metalcarboxylate salts, cyano moieties and trihalomethyl moieties. The mostpreferred electron-deficient carbon groups are carboxyls and acylhalides. The halogen incorporated in electron-deficient carbon groups ispreferably chlorine, bromine or iodine and most preferably chlorine.

Functional group--A group that function as a reactive site during a PBZpolymerization reaction. Functional groups in a PBZ polymerizationreaction are selected from the group consisting of electron-deficientcarbon groups and o-amino-basic moieties as both of those terms aredefined herein. Functional groups can be located on PBZ monomers, PBZoligomers, terminating agents, branching agents, and reaction productsresulting from combinations of the same.

o-Amino-basic moiety--A moiety which can react with anelectron-deficient carbon group in a suitable dehydrating solvent toform an azole ring. An o-amino-basic moiety comprises two componentsbonded to an aromatic group. One component is a primary amine group andthe second component is a --ZH group. These components are bonded to thearomatic group in a position ortho with respect to each other. The Z ofthe --ZH group is O, S or NR, R being selected from the group consistingof hydrogen, aliphatic groups containing up to about 12 carbon atoms,and aromatic groups containing up to about 18 carbon atoms. The --ZHgroup suitably comprises a hydroxy, thiol, primary amine, or secondaryamine group; preferably a hydroxy or thiol group; and most preferably ahydroxy group. Where the --ZH group is a secondary amine grouprepresented by the formula NR, R is suitably an aromatic or an aliphaticgroup, preferably an alkyl group. The secondary amine group preferablycomprises no more than about 6 carbon atoms, more preferably no morethan about 4 carbon atoms and most preferably 1 carbon atom.

PBZ monomer--An AA- , AB- and BB- monomer (as those terms are definedhereinafter) that can react in a PBZ polymerization reaction to producea PBZ polymer. The terms AA-, AB- and BB- monomer are generally used inthe art, such as in 11 Ency. Poly. Sci. & Eng., previously incorporatedby reference herein.

PBZ polymer--A polybenzazole (PBZ) polymer is a polymer selected fromthe group consisting of polybenzoxazoles and polybenzobisoxazoles(collectively referred to hereinafter as PBO); polybenzothiazoles andpolybenzobisthiazoles (collectively referred to hereinafter as PBT); andpolybenzimidazoles and polybenzobisimidazoles (collectively referred tohereinafter as PBI), the nomenclature of which is discussed in 11 Ency.Poly. Sci. & Eng., supra, pp. 601-603, previously incorporated herein byreference. For purposes of this application, the term "PBZ polymer"refers broadly to polymers comprising repeating units (herein referredto as a "mer unit" ) that contain an azole ring which is fused, bondedor both fused and bonded to an aromatic group. The aromatic group is notnecessarily limited to a single 6-membered carbon ring. The term "PBZpolymer" also refers broadly to poly(phenylene-benzo-bis-azole)s andsimilar polymers wherein each mer unit comprises a plurality of azolerings fused to an aromatic group.

II. Synthesis of Branched PBZ Polymers

A branched PBZ polymer according to the present invention can besynthesized by reacting at least one branching agent with at least onePBZ monomer or a chain of PBZ mer units in a dehydrating solvent.Techniques known within the art for conducting PBZ polymerizations, suchas those described within the Wolfe patents incorporated by referenceherein, are in general applicable in making branched PBZ polymers. Forexample, a branched PBZ polymer may be formed by the condensationpolymerization of at least one branching agent with at least oneAB-monomer. Branched PBZ polymers may also be synthesized by reaction ofat least one branching agent with a combination of at least oneAA-monomer and at least one BB-monomer. Other variations will becomeapparent to the reader upon review of the disclosure herein.

A. Branching Agents Useful in Practicing the Invention

A branching agent comprises an organic multivalent base structure moietywith at least three azole-forming moieties randomly attached thereto.Each azole-forming moiety is capable of reacting with anotherazole-forming moiety on a PBZ monomer or a PBZ oligomer to form an azolering and product reaction products. Branching agents may also react withavailable azole-forming moieties on such reaction products to produce alarger molecule, and so on. Branching agents used in the reactionpreferably cannot react with each other and therefore, containfunctional groups consisting of either all electron-deficient carbongroups or all o-amino-basic moieties.

The choice of base structure moiety is not critical, so long as it isstable and inert with respect to the condensation polymerizationreaction conditions and does not substantially interfere with azole ringforming reactions between functional groups as previously described. Asuitable base structure moiety can be aliphatic, alicyclic or aromatic.Preferred base structure moieties are aromatic in nature and mostpreferably correspond to the description and preferred embodimentspreviously given for aromatic groups. Branching agents preferably have anumber average molecular weight of no greater than about 500.

Each functional group on a base structure moiety will preferably reactwith a PBZ monomer or a PBZ oligomer such that a PBZ polymer branch isformed at the site of each functional group existing prior topolymerization. Those persons skilled in the art will recognize thatsome functional groups may not react during polymerization. However, itis desirable that at least three functional groups of a branching agentbase structure moiety react with a PBZ oligomer to yield a branchedpolymer structure.

Positioning of the functional groups on the base structure moiety is notcritical, as long as the positioning does not lead to reaction betweenadjacent functional groups when a branching agent contains bothelectron-deficient carbon groups and o-amino-basic moieties, or preventreaction of a functional group. Preferred branching agents preferablyhave functional groups positioned equidistance from each other on thebase structure moiety. Examples of preferred branching agents are1,3,5-benzenetricarboxylic acid and 1,3,5-benzentricarbonyl trichloride.The tetra-functional carboxylic acid depicted in Formula 2 is an exampleof another preferred branching agent. ##STR3##

Additional examples of suitable branching agents are novel compoundshaving structures shown in Formulas 3(a)-(c) below: ##STR4## wherein:Ar¹ is a first aromatic group;

Ar² is a second aromatic group;

p¹⁻⁴ are each functional groups; and

Z, Z¹ and Z² are each selected from O, S, or NR, where R is selectedfrom the group consisting of hydrogen, aliphatic groups containing up toabout 12 carbon atoms and aromatic groups containing up to about 18carbon atoms. The description and preferred embodiments for Ar¹ and Ar²are those previously given for aromatic groups. The aromatic groups Ar¹and Ar² can be the same or different, but are most preferably bothsingle benzene rings. The description and preferred embodiments for P¹⁻⁴correspond to those previously given for electron-deficient carbongroups and o-amino-basic moieties. The description and preferredembodiments of Z groups are those as previously described in definingo-amino-basic moieties.

Compounds 3(a) and 3(b) are formed by the reaction of a compoundcontaining at least three azole-forming moieties with a compoundcontaining two azole-forming moieties. Compound 3(c) is obtained byreacting an AB-monomer with a tri-functional compound.

Tetra-functional branching agents, such as those illustrated by Formula2, can be synthesized by reacting a BB-monomer with a compound havingthree electron-deficient carbon groups. Examples of suitable compoundsare 1,3,5-benzenetricarboxylic acid and 1,3,5-benzenetricarbonyltrichloride. The reaction is illustrated by the following equation givenas an example: ##STR5## The reaction is conducted in a dehydratingsolvent, such as polyphosphoric acid, using the techniques previouslyincorporated by reference and described hereinafter in relation to PBZpolymerization reactions. Tetrafunctional branching agents correspondingto Formulas 3(a) and (b) can also be synthesized in the same manner byreacting an AA-monomer with a compound having three o-amino-basicmoieties.

Those skilled in the art will recognize that the tetra-functionalbranching agents illustrated by Formula 3(a) and (b) are averagestructures. In Formula 2, for example, another BB-monomer may react withan available electron-deficient carbon group to produce a branchingagent with five functional groups, and so on. However, it is believedthat the illustrative reaction yields a product consisting predominantlyof the tetrafunctional carboxylic acid. These compounds can then bepolymerized with PBZ monomers in a subsequent condensationpolymerization to produce a branched PBZ polymer.

The tri-functional branching agents as shown in Formula 3(c) may besynthesized by reacting an AB-monomer with a compound having threeazole-forming moieties. Examples of suitable compounds having threeelectron-deficient carbon groups are 1,3,5-benzentricarboxylic acid and1,3,5-benzenetricarbonyl trichloride. The reaction is illustrated by thefollowing equation given as an example: ##STR6## As in the reactionpreviously illustrated for the tetrafunctional branching agents, thisreaction is conducted in a dehydrating solvent, such as polyphosphoricacid, using the techniques previously incorporated by reference and asdescribed hereinafter relating to PBZ polymerization reactions.Synthesis of a tri-functional branching agent can also be performed inthe same manner by reacting an AB-monomer with a compound having threeo-amino-basic moieties.

Those skilled in the art will recognize that the tri-functionalbranching agents illustrated by Formula 4 are average structures. Forexample, another AB-monomer may react with an available P group and soon. However, it is believed that the illustrative reaction set forthabove yields a product consisting predominantly of the tri-functionalcarboxylic acid. These compounds, like the tetra-functional compoundspreviously described, can be polymerized with PBZ monomers to produce abranched PBZ polymer.

Persons skilled in the art will recognize that many compounds can act asa branching agent to produce the branched PBZ polymers of the presentinvention, provided such compounds contain appropriate functional groupsand other substituents previously described which will permit reactionof the azole-forming moieties.

Each branching agent may contain substituents on the base structuremoiety which are stable with respect to reagents and solvents used inthe polymerization and do not interfere with reaction of the attachedfunctional groups. Examples of suitable substituents include hydrogen,halogens, alkoxy moieties, aryloxy moieties and alkyl groups. Preferredsubstituents are hydrogen, halogens and alkyl groups having up to about6 carbon atoms. Hydrogen and alkyl groups are the most preferredsubstituents.

Control over the degree of branching within a reaction product isnecessary to obtain a branched PBZ polymer dope with sufficientductility to allow formation of useful objects by extrusion methodsdescribed hereinafter. The degree of branching may also vary thephysical properties of the resulting branched polymer. If the degree ofbranching is not limited, the branched PBZ polymer dope will becomecross-linked and incapable of being processed into useful articles ofmanufacture such as fibers, films or the like. Use of an excess ofbranching agent will produce branched PBZ polymer dopes that, whenextruded through a die, break into a fibrous non-agglomerated mass.

The degree of branching can be varied by choosing the number offunctional groups on the branching agent, i.e. the branching agent'sdegree of functionality, by varying the amount of branching agentutilized in the polymerization, or by a combination thereof. In general,a higher degree of functionality will reduce the amount of branchingagent required to obtain a desired degree of branching in the finalproduct. Conversely, a lower degree of functionality will increase theamount of branching agent necessary to obtain the same degree ofbranching.

In terms of mole percentages of reactants prior to polymerization, theamount of branching agent is suitable less than about 14 mole %, butgreater than about 0.05 mole %. The amount is preferably less than about5 mole % and most preferably less than about 2 mole %.

It is believed that the length of individual PBZ polymer branches can bevaried by using a branching agent having at least two differentfunctional groups that have differing reaction rates with respect to thePBZ monomers being polymerized.

B. PBZ Monomers Useful in Practicing the Invention

Any PBZ monomer described in the Wolfe patents previously incorporatedherein by reference may be used to prepare a branched PBZ polymeraccording to the present invention. Each monomer classification isdescribed hereinafter.

An AB-monomer independently comprises an aromatic group (Ar) which hasrandomly attached thereto both an o-amino-basic moiety and anelectron-deficient carbon group. The term "AB-monomer" corresponds withterminology commonly used within the art, such as that found in 11 Ency.Poly. Sci. & Eng., supra, previously incorporated herein by reference.The "A" refers to electron-deficient carbon group functionality and the"B" refers to o-amino-basic functionality. The electron deficient carbongroup is preferably in a position para with respect to either theprimary amine group or the --ZH moiety components of the o-amino-basicmoiety.

Illustrative AB-monomers are represented by Formulas 4 (a) and (b) whereQ and --ZH are as previously defined. ##STR7##

Examples of preferred AB-monomers are 3-hydroxy-4-aminobenzoic acid or3-amino-4-hydroxybenzoic acid. Other suitable examples of AB-monomersare those listed in U.S. Pat. No. 4,533,693 columns 33-35 at Table 8,the teachings of which are incorporated herein by reference.

A BB-monomer as referred to herein comprises an aromatic group (Ar)which has bonded thereto two o-amino-basic moieties. The term "BB" iscommonly used in the art and refers to the presence of two o-amino-basicmoiety functional groups.

Examples of suitable BB-monomers and reference to their synthesis arefound in U.S. Pat. No. 4,533,693, Table 1, columns 19-21 and Tables 2and 3, columns 21-22 and 23-24; Lysenko, High Purity Process for thePreparation of 4,6-Diamino-1,3-Benzenediol, U.S. Pat. No. 4,766,244(Aug. 23, 1988); and Inbasekaran, Preparation of Diamino- andDialkylaminobenzenediols, U.S. Pat. No. 4,806,688 (Feb. 21, 1989). Theseexamples of BB-monomers are incorporated herein by reference.BB-monomers preferably comprise a single benzene ring with theo-amino-basic moieties in a 1,2- and 4,5- position on the ring. Examplesof preferred linear BB-monomers are 4,6-diaminoresorcinol and2,5-diamino-1,4-benzenediol.

An AA-monomer comprises an intermediate moiety, as that term is definedhereinabove in relation to the term aromatic group, having bondedthereto two electron-deficient carbon groups. With respect toAA-monomers, preferred intermediate moieties are aromatic groups. Theintermediate moiety itself is inert during a PBZ condensationpolymerization. The term "AA" is commonly used in the art and refers tothe presence of two electron-deficient carbon groups.

Examples of suitable AA-monomers and reference to their synthesis arefound in U.S. Pat. No. 4,533,693 Table 4, Table 5 and Table 6 in Col.25-32. These examples of AA-monomers are incorporated herein byreference. Examples of preferred AA-monomers are terephthalic acid,terephthaloyl chloride, 4,4'-biphenyldicarboxylic acid and4,4'-biphenyldicarbonyl dichloride.

Monomers of the AB- and BB- types are generally stored as salts topreclude oxidative degradation of the o-amino-basic moiety functionalgroups. These monomers are preferably stored as hydrogen halide salts,but suitable practice is to isolate and store the monomers in the formof other mineral acid salts, such as salts of sulfuric, nitric orphosphoric acid. Certain phosphate salt are discussed in our copendingapplication, Ser. No. 341,501. Phosphate and other mineral acid saltsare discussed in the Lysenko patent, supra, at column 4, lines 40-44 andImai et al., "Polybenzazoles", 83 Makromol. Chem. 179-187 (1965), theteachings of which are incorporated herein by reference.

C. Reaction of PBZ Monomers and Branching Agents According to theInvention

Techniques for reacting AB-, AA- and BB-monomers in a condensationpolymerization are discussed at length in 11 Ency. Poly. Sci. & Eng.,supra, at 611-19, as well as U.S. Pat. Nos. 4,703,103; 4,533,724;4,533,692; 4,533,693; and 4,578,432, the teachings of which areincorporated herein by reference.

The polymerization preferably takes place in a dehydrating solvent asthat term is previously defined. A preferred dehydrating solvent is adehydrating mineral acid such as polyphosphoric acid. If a nonrigid-rodPBZ polymer or a low molecular weight rigid-rod PBZ polymer is desired,it is believed that a nondehydrating solvent may be employed.

If a branched PBZ polymer of high molecular weight is desired in aliquid crystalline, or anisotropic solution, the P₂ O₅ content of thepolyphosphoric acid solvent may be controlled as described in U.S. Pat.No. 4,533,693, column 42, line 61 to column 45, line 52, the teachingsof which are incorporated herein by reference. When a high molecularweight polymer is desired, the polyphosphoric acid initially contains atleast about 73% by weight P₂ O₅ as described hereinabove. If PBZmonomers in the form of hydrogen halide salts are employed, a lowerinitial P₂ O₅ content lowers solution viscosity and reduces foamingassociated with the release of hydrogen halide gas during initial stagesof the polymerization, a technique typically referred to in the art as adehydrohalogenation step. After dehydrohalogenation, the P₂ O₅ contentis preferably increased so that the P₂ O₅ content after polymerizationis at least about 80% by weight.

The condensation polymerization reaction is typically performed under aninert atmosphere, for instance under nitrogen, argon or helium, withnitrogen being preferred. The inert atmosphere is required to preventair oxidation of AB- or BB-monomers used in the reaction.

The reaction pressure is not critical, as long as the solvent remainssubstantially in a liquid phase. However, pressure can be reduced duringthe reaction to encourage release of hydrogen halide gas formed duringdehydrohalogenation of AB- and BB-monomers.

The temperature during the initial dehydrohalogenation step, if such astep is employed, should be sufficient to initiate release of hydrogenhalide gas. The temperature is preferably from about 25° C. to about100° C., and more preferably about 45° C. The preferred temperaturerange specified for dehydrohalogenation can be sufficient to begin thecondensation polymerization reaction. Some monomers, such asterephthaloyl chloride, can sublime at higher temperatures. Therefore,when using sublimable monomers it is advantageous to have a temperaturewithin this preferred range for a time sufficient to allow formation ofPBZ oligomers and thereby reduce monomer loss by sublimation at highertemperatures. Thereafter, the temperature is preferably increased toenhance the rate of reaction.

Many monomers, such as terephthalic acid and 4,4'-bis(benzoic acid), areonly slightly soluble in dehydrating solvents and therefore vigorousagitation is required to enhance dissolution of the monomer. Due to poormonomer solubility, the mixture of reactants and solvent more closelyresembles a suspension reaction temperatures.

After dehydrohalogenation, the reaction temperature is beneficiallyraised to a level sufficient to promote condensation polymerization andobtain branched PBZ polymers of greater molecular weight. The reactiontemperature is suitably at least about 70° C., desirably at least about95° C., preferably at least about 150° C. and most preferably at leastabout 190° C. However, the maximum temperature of the reaction may beany temperature at which the polymer and solvent are stable. The maximumtemperature is desirably no more than about 240° C., preferably no morethan about 225° C. and most preferably no more than about 210° C. If thetemperature is too low, an uneconomically long time is needed to formthe desired branched PBZ polymers. Excessively high temperatures favormonomer degradation, monomer sublimitation or undesired side reactionswhich will adversely impact molecular weight in the resulting polymer.

The time required to obtain a desired degree of polymerization varieswidely depending upon the reactions and temperatures used as is known topersons of ordinary skill in the art of PBZ polymers. The reactionpreferably proceeds at a temperature of from about 190° C. and 210° C.for at least about 30 minutes. A longer or shorter time period may beused if desired.

PBZ monomers used in practicing the present invention are preferably inthe form of a combination of at least one AA-monomer and at least oneBB-monomer as previously described. An excess of BB-monomer yields shortpolymer chains forming the PBZ polymer branches with a correspondinglylow molecular weight. An excess of AA-monomer in less than about a 10mole % excess surprisingly does not substantially effect polymermolecular weight. An excess of AA-monomer greater than about 10 mole %is unnecessary and difficult to remove. In preferred embodiments of thepresent invention, neither the BB- nor the AA-monomer is present in morethan about a 10% molar excess. These monomers are more preferably in nomore than about a 5% molar excess and most preferably no more than abouta 1% molar excess. If the reaction is performed with an excess of amonomer, the excess is preferably less than about 1 mole % ofBB-monomer.

Brnched PBZ polymers can be synthesized in any concentration which thedehydrating solvent is capable of dissolving. The concentration ofbranched polymer is suitably from about 1% by weight to about 20% byweight and preferably from about 4% by weight to about 18% by weight.Concentrations below about 1% by weight are economically undesirable. Itis generally difficult to obtain concentrations in excess of 20% byweight, because of the handling problems associated with high viscositysolutions. Where polyphosphoric acid or methanesulfonic acid with addedP₂ O₅ is the dehydrating solvent, the concentration of branched PBZpolymer in the solvent is typically less than about 20% by weight.However, it is believed that the 20% limit can be exceeded by decreasingthe molecular weight of the branched PBZ polymer.

The PBZ condensation reaction produces a dope comprising at least onedehydrating solvent and a branched PBZ polymer. Dopes obtained inpracticing the present invention can be either isotropic or anisotropic.The dividing line between isotropic and anisotropic solutions varieswith each particular branched PBZ polymer, the polymer concentration,the polymer molecular weight, the solution temperature and the solvent.In general, a dividing line between an anisotropic solution and anisotropic solution occurs at a branched PBZ polymer concentration ofabout 5% by weight. Concentrations below about 5% by weight generallyproduce isotropic solutions, while those above about 5% by weightproduce anistropic or liquid crystalline solutions. An isotropicsolution is suitable for fabrication of molecular composites. Ananistropic solution is suitable for use in making fibers or films.

D. Control of the Degree of Branching and Branch Length

The degree of branching within a branched PBZ polymer and the length ofPBZ polymer branches can be further controlled by addition of at leastone terminating agent prior to reaching the desired degree ofpolymerization. The terminating agent is preferably added prior tobeginning the polymerization to achieve maximum control over the degreeof branching. As mentioned above, control over the degree of branchingis necessary to obtain a PBZ polymer dope capable of being processedinto useful articles. A terminating agent is also useful to controlbranch length and molecular weight. The terminating agent may furtherinfluence physical properties in the resultant branched PBZ polymer.

A terminating agent suitably comprises a base structure that hasattached thereto a functional group selected from the group consistingof o-amino-basic moieties and electron-deficient carbon groups. Thechoice of base structure is not critical so long as it is inert withrespect to the polymerization reaction. The functional group can bechosen to react with a given monomer, a group of monomers, a branchingagent and so on. The choice depends upon the functional groups appearingon the given monomer or branching agent. The use of monofunctionalreactants, i.e. terminating agents, in a PBZ polymerization reaction isgenerally discussed in U.S. Pat. No. 4,703,103 at column 41, line 25 tocolumn 47, line 64, the teachings of which are incorporated herein byreference. Upon reaction of the functional group, the remaining portionof the terminating agent molecule not altered by the reaction becomes aterminating end group.

Examples of suitable terminating agents useful in practicing the presentinvention are identified in Tables 15 (a)-(c) of the U.S. Pat. No.4,703, 103 patent previously incorporated by reference herein. Preferredterminating agents are benzoic acid, benzoyl chloride, o-amino phenol,o-amino-thiophenol, and o-diaminobenzene.

The amount of terminating agent will vary widely depending upon theamounts of other reactants and the desired molecular weight of thebranched PBZ polymer product. In general, it is advantageous to use lessthan 10 mole %. The amount is desirably less than about 5 mole % andpreferably less than about 2 mole %.

III. Branched PBZ Polymers of the Invention

The branched PBZ polymers formed as a result of the reaction comprise aplurality of base structure moieties having a plurality of, preferablyat least three, chain-like PBZ polymer branches bonded thereto. It isbelieved that branched PBZ polymers based solely upon AB-monomers arediscrete entities having no interconnection or bonding with other basestructure moieties or PBZ polymers. Other PBZ polymers, e.g. thoseproduced by polymerizing a mixture of AA- and BB- monomers, may havesome chemical bonding. For example, two base structure moieties mayshare a common AA/BB-PBZ polymer branch.

The PBZ polymer branches of the present invention suitably comprise, onaverage, from about 10 PBZ mer units to about 500 PBZ mer units. Thebranches preferably have from about 20 PBZ mer units to about 100 PBZmer units. Each PBZ mer unit comprises:

(1) an aromatic group (Ar); and

(2) a first azole ring which is fused with the aromatic group.

Each PBZ mer unit preferably further comprises:

(3) a second azole ring which is fused with the aromatic group, and

(4) an intermediate moiety, as that term is defined herein, covalentlybonded by a single bond to the 2-carbon of the second azole ring.

Each aromatic group independently has the definition and preferredembodiments previously described for aromatic groups. Each intermediatemoiety independently has the definition and preferred embodiments forintermediate moieties in AA-monomers. Preferred PBZ polymer branches arethose selected from the group consisting of PBO polymers and PBTpolymers, as those terms are previously defined.

If the PBZ mer units have only a single azole ring per unit (referred toherein as AB-PBZ mer units), then individual mer units are preferablylinked by a single bond from the 2-carbon of the azole ring to the firstaromatic group of an adjacent unit. If the PBZ mer units have two azolerings per unit and an intermediate moiety (referred to herein asAA/BB-PBZ mer units), then individual units are preferably linked by asingle bond from the intermediate moiety to the 2-carbon in the firstazole group of an adjacent unit.

Chains of PBZ mer units comprising the branches of the present inventioncan be formed by reacting a mixture of Ab-, AA- and BB monomer. The PBZpolymer branches formed by reacting this mixture comprise copolymerchains with randomly spaced AB-PBZ and AA/BB-PBZ mer units.

Chains of PBZ mer units can be formed by reacting a mixture of AA- andAB-monomers. This reaction is expected to place only one AA-monomermoiety within a single branch. As such, these branches should closelyresemble branches formed solely from AB-monomers.

At least one AB-monomer can be reacted with at least one branching agentto form an intermediate polymer comprising branches of repeating AB-PBZmer units. This intermediate can then be reacted with at least oneAA-monomer and at least one BB-monomer to produce a branched PBZ polymercontaining some branches consisting of AB-PBZ mer units and somebranches consisting of a block of AB-PBZ mer units followed by a blockof AA/BB-PBZ mer units.

Conversely, at least one AA-monomer, at least one BB-monomer and atleast one branching agent can react to form an intermediate branchedAA/BB-PBZ polymer. This intermediate can than be reacted with at leastone AB-monomer to produce a branched PBZ polymer containing somebranches consisting of AA/BB-PBZ mer units and some branches consistingof blocks of AA/BB-PBZ mer units followed by blocks of AB-PBZ mer units.

Many variations in the manner of reacting AB-, AA- and BB-monomers willbecome apparent to those skilled in the art. All of these variations areintended to come within the scope of the present invention.

Branched PBZ polymers formed in practicing the present inventionsuitable have a number average molecular weight of at least 5,000. Thenumber average molecular weight beneficially ranges from 5,000 to500,000. Molecular weights above and below this range are possible, butmay not be economically advantageous. The actual molecular weight willvary depending upon the particular polymer structure synthesized and itsintended end use. Those skilled in the art of PBZ polymers measuremolecular weight of a PBZ polymer by its inherent viscosity whendissolved in a solvent, such as methanesulfonic acid, a technique whichis generally described in 11 Ency. Poly. Sci. & Eng., supra, at page623. Branched PBZ polymers, produced in the form of an isotropicsolution, suitable have an inherent viscosity of at least about 0.5dL/g, when measured at 25° C. in methanesulfonic acid and a polymerconcentration of between about 0.05 g/dL and about 0.5 g/dL. BranchedPBZ polymers, produced in the form of an anisotropic solution, suitablyhave an inherent viscosity of at least about 5 dL/g, and desirably atleast about 10 dL/g, when measured at 25° C. in methanesulfonic acid anda polymer concentration of between about 0.005 and about 0.5 g/dL.

The branched PBZ polymer formed as a result of the previously describedcondensation reaction can be isolated from the resulting dope, asdescribed in greater detail hereinafter, by the addition of anon-solvent for the polymer which is miscible with the dehydratingsolvent. A preferred non-solvent is water when polyphosphoric acid isthe dehydrating solvent.

Branched PBZ polymers of the present invention, after isolation from thedope, can be processed into powders by methods known in the art, such ascoagulation of the dope in a high shear medium or grinding.Alternatively, they may be extruded as fibers and films as describedhereinafter.

IV. Fabrication of Articles of Manufacture Containing Branched PBZPolymers

The branched PBZ polymer compositions of the present invention can befabricated into an article of manufacture, such as a fiber or film. Thearticles exhibit the expected high tensile modulus and tensile strengthexpected from PBZ polymers. Fibers and films may be formed from eitherisotropic or anisotropic dopes as previously described. The dopes mayresult from first isolating the branched polymer from a dope formedduring polymerization and subsequently redissolving the polymer inanother solvent which may or may not be a dehydrating solvent. The dopesare more practically the direct product of the process previouslydescribed for making branched PBZ polymers.

The branched PBZ polymer dopes are preferably degassed at elevatedtemperature and under reduced pressure, such as about 80° C. and about0.4 in Hg, to remove any residual hydrogen halide gas or inert gasremaining after synthesis prior to further processing.

Fibers are spun from the degassed dopes according to techniques familiarto persons of ordinary skill in the art. See, e.g., 11 Ency. Poly. Sci.& Eng., supra, at 625-28; U.S. Pat. No. 4,533,693 at columns 82-84,Hwang et al., "Solution Processing and Properties of Molecular CompositeFibers and Films," 23 Poly. Eng. & Sci. 784, 785 (1984); and Hwang etal., "Composites on a Molecular Level: Phase Relationships, Processing,and Properties," B22 (2) J. Macromol. Sci. & Phys. 231, 234-35 (1983),the teachings of which are incorporated herein by reference. The dopecan, for example, be forced through a temperature-controlled spinneretteby a piston, or other dope forwarding device, which extrudes the dope asa number of thin streams. Other conventional methods may be used torecover the polymer and form fiber and films therefrom.

SPECIFIC EMBODIMENTS OF THE INVENTION

The following examples illustrate the present invention and should notbe construed, by implication or otherwise, as limiting the scopethereof. All parts and percentages are by weight and all temperaturesare in degrees centigrade (°C.) unless otherwise indicated.

EXAMPLE 1 Preparation of Branched AA/BB-PBO Polymers S

In a nitrogen environment, measured amounts of the reactants4,6-diaminoresorcinol dihydrochloride (DAHB) (a BB-monomer),terephthaloyl chloride (TC) (an AA-monomer), and1,3,5-benzenetricarboxylic acid (TMA) (a branching agent), and apolyphosphoric acid (PPA) dehydrating solvent containing about 76% byweight P₂ O₅ are loaded into a resin kettle. Amounts used for reactantsand solvent in each experimental run are given in Table 1. Generallyfollowing the procedures taught by U.S. Pat. No. 4,533,693, theabove-identified reactants and solvent are vigorously agitated at atemperature of about 45° C. and atmospheric pressure for approximately16 hours. The resulting solutions are then heated to about 95° C. and P₂O₅ is added to the kettle in an amount as shown in Table 1. Thesolutions foam as hydrogen chloride gas is released and turn yellow incolor. The reactions continue at atmospheric pressure with agitation forabout 24 hours at 95° C., a subsequent 54 hours at 150° C., and a final24 hours at 190° C. The resulting dopes for each run are stored under anitrogen atmosphere until needed.

To measure inherent viscosity (n_(inh)) in each run, the respectivebranched polymer is isolated by coagulating the dope produced in the runin a water bath. The product is dried, acid extracted with water in aSoxhlet extractor, ground to a fine powder, reextracted with water, andgiven a final drying at about 170° C. and 3.0 mm Hg. The dried, branchedpolymer product is dissolved at room temperature in methanesulfonic acidto obtain a solution having a concentration of about 0.05 g/dL. Theinherent viscosity of the solution at 25° C. is measured in aSchott-Gerate CT 150 bath in an Ubelhobde tube. The inherent viscosityshown for the polymer synthesized in each run is shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________    Experimental Data for AA/BB-PBO Polymer Synthesis                             Experimental                                                                         DAHB                                                                              DAHB                                                                              TC  TC  TMA TMA PPA P.sub.2 O.sub.5 Added                                                                ηinh                            Run    (g) (mmol)                                                                            (g) (mmol)                                                                            (g) (mmol)                                                                            (g) (g)    dL/g                                __________________________________________________________________________    A      10.00                                                                             46.9                                                                              9.52                                                                              46.9                                                                              0.07                                                                              0.3 42.9                                                                              28.9   17.0                                B      116.10                                                                            545 110.99                                                                            547  0.464                                                                             2.21                                                                             498.0                                                                             335.5  21.3                                C      10.00                                                                             46.9                                                                              9.56                                                                              47.1                                                                              0.04                                                                              0.2 45.4                                                                              26.4   12.0                                D      10.00                                                                             46.9                                                                              9.56                                                                              47.1                                                                              0.04                                                                              0.2 42.9                                                                              28.9   23.4                                __________________________________________________________________________

EXAMPLE 2 Preparation of Branched AB-PBO Polymers

In a nitrogen atmosphere, measured amounts of the reactants3-amino-4-hydroxybenzoic acid hydrochloride monohydrate (AHB) (anAB-monomer) and 1,3,5-benzenetricarboxylic acid (TMA) and apolyphosphoric acid (PPA) solvent containing about 76% by weight P₂ O₅are loaded into a resin kettle. The measured amounts of reactants andsolvent used for two experimental runs are given in Table 2. Afterheating and agitating the reactants and solvent for about 16 hours at45° C., an added amount of P₂ O₅ is introduced into the kettle. Theresulting solutions are reacted according to the procedure used inExample 1. The inherent viscosity, measured according to the procedureused in Example 1, is shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Experimental Data for AB-PBO Polymer Synthesis                                Using Trimesic Acid as a Branching Agent                                      Experi-                                P.sub.2 O.sub.5                        mental                                                                              AHB     AHB     TMA   TMA   PPA  Added ηihn                         Run   (g)     (mmol)  (g)   (mmol)                                                                              (g)  (g)   (dL/g)                           ______________________________________                                        A     59.24   286     1.00  4.76  103.0                                                                              105.2 3.08                             B     29.62   143     1.00  4.76   48.7                                                                               55.3 2.20                             ______________________________________                                    

EXAMPLE 3 Preparation of Branched AB-PBO Polymers with a DifferentBranching Agent

To illustrate the use of another compound as a branching agent, theprocedure of Example 2 is duplicated with the exception of reagentamounts. A 0.10 g (0.38 mmoles) amount of 1,3,5-benzenetricarbonyltrichloride as a branching agent, a 25.00 g (120.5 mmoles) amount of3-amino-4-hydroxybenzoic acid hydrochloride monohydrate (an AB-Monomer)and 24.3 g of a polyphosphoric acid dehydrating solvent with a P₂ O₅content of about 77% by weight are introduced into a resin kettle. Uponheating to 95° C., 38.4 g of added P₂ O₅ is introduced to the kettle asin the previous runs. The inherent viscosity measured as in Example 1for the resulting polymer is 10.0 dL/g.

EXAMPLE 4 Preparation of Branched PBO Polymers With Branches Consistingof Blocks of AA/BB-PBO and AB-PBO Mer Units

In a nitrogen environment, a solution is formed by loading and mixing ina resin kettle 10.00 g (46.94 mmoles) of 4,6-diaminoresorcinoldihydrochloride (a BB-monomer), 9.56 g (47.08 mmoles) of terephthaloylchloride (an AA-monomer) and 4.18 g of the branched AB-PBO polymer dopeprepared in Example 2B. The branched AB-PBO polymer synthesized inExample 2B has branches consisting of, based upon a calculated average,of about 10 PBO mer units. The above-described mixture of reactants andsolvent is reacted following the procedure used in Example 1. Thepolymer is isolated from the dope and the inherent viscosity measuredaccording to the procedures used in Example 1. The measured inherentviscosity is 19.7 dL/g.

EXAMPLE 5 Replication of Example 4 Based upon Material Prepared inExample 2A

The procedure of Example 4 is replicated for experimental runs A and B,except for deviation in procedure with respect to conducting the laterstages of the reaction for run B in a piston reactor. In runs A and B,the AB-PBO dope used is that prepared in Example 2A. The branched AB-PBOpolymer synthesized in Example 2A has branches consisting of acalculated average of about 20 PBO mer units.

After about two hours at 150° C. for sample run B, the contents of theresin kettle are transferred to a piston reactor where the reaction iscontinued and the dope is spun into fiber. The amount of reactants andsolvent used for both sample runs, as well as measured inherentviscosities are set forth in Table 3.

                                      TABLE 3                                     __________________________________________________________________________    Experimental Data for PBO Polymers Synthesized with Blocks of                 AA/BB-PBO and AB-PBO Mer Units                                                                       AB-PBO       P.sub.2 O.sub.5                           Experimental                                                                         DAHB                                                                              DAHB                                                                              TC  TC  dope AB-PBO                                                                             PPA                                                                              Added                                                                             ηinh                              Run    (g) (mmol)                                                                            (g) (mmol)                                                                            (g)  (mmol)                                                                             (g)                                                                              (g) dL/g                                  __________________________________________________________________________    A       7.50                                                                             35.2                                                                               7.17                                                                              35.3                                                                              7.83                                                                              0.141                                                                               33.3                                                                             20.6                                                                             26.6                                  B      115.00                                                                            539.75                                                                            109.94                                                                            541.5                                                                             120.06                                                                             2.17 510.6                                                                            315.9                                                                             19.0                                  __________________________________________________________________________

The data shown in Table 3 illustrate preparation of a branched PBZpolymer with a AB-PBO block connected to an AA/BB-PBO block. Similarresults are expected with other compositions disclosed hereinabove.

EXAMPLE 6 Preparation of Branched PBO Polymers with Mono-FunctionalTerminating Agents

In a nitrogen environment, measured amounts of the reactants4,6-diaminoresorcinol dihydrochloride (DAHB), terephthaloyl chloride(TC), 1,3,5-benzenetricarboxylic acid (TMA), benzoic acid (BA) and apolyphosphoric acid (PPA) dehydrating solvent containing about 76% byweight P₂ O₅ are loaded into a resin kettle. Amounts used for reactantsand solvent in each experimental run are given in Table 4. The resultingsolutions are reacted as in Example 1. The inherent viscosities of thepolymers are measured as in Example 1 and are given in Table 4.

                                      TABLE 4                                     __________________________________________________________________________    Experimental Data For Synthesis of Branched PBO Polymers                      Using Benzoic Acid as a Terminating Agent                                                                              P.sub.2 O.sub.5                      Experimental                                                                         DAHB                                                                              DAHB                                                                              TC  TC  TMA TMA BA BA  PPA                                                                              Added                                                                             ηinh                         Run    (g) (mmol)                                                                            (g) (mmol)                                                                            (g) (mmol)                                                                            (g)                                                                              (mmol)                                                                            (g)                                                                              (g) dL/g                             __________________________________________________________________________    A      10.00                                                                             46.94                                                                             9.50                                                                              46.79                                                                             0.086                                                                             0.41                                                                              0.050                                                                            0.41                                                                              43.1                                                                             28.7                                                                              12.3                             B      10.00                                                                             46.94                                                                             9.50                                                                              46.79                                                                             0.086                                                                             0.41                                                                              0.150                                                                            1.23                                                                              43.1                                                                             28.7                                                                              8.14                             C       7.50                                                                             35.21                                                                             6.58                                                                              32.39                                                                             0.148                                                                              0.704                                                                            0.086                                                                             0.704                                                                            34.1                                                                             19.8                                                                              4.28                             D      10.00                                                                             46.94                                                                             9.37                                                                              45.71                                                                             0.040                                                                             0.20                                                                              0.073                                                                            0.60                                                                              42.9                                                                             28.9                                                                              12.5                             E      115.00                                                                            540 109.25                                                                            538 0.989                                                                             4.71                                                                              0.575                                                                            4.71                                                                              521.8                                                                            304.0                                                                             10.6                             F      116.10                                                                            544.9                                                                             110.99                                                                            546.7                                                                             0.464                                                                             2.21                                                                              0.270                                                                            2.21                                                                              500.7                                                                            333.0                                                                             12.4                             __________________________________________________________________________

The data shown in Table 4 illustrate the use of mono-functionalterminating agents in a branched PBZ polymerization.

EXAMPLE 7 Preparation of Tetra-Functional Branching Agents

In a nitrogen environment, a solution is formed by loading into a 100 mlresin kettle, and thereafter mixing, 2.00 g (18.77 mmoles) of4,6-diaminoresorcinol dihydrochloride and 3.94 g (37.55 mmoles) of1,3,5-benzenetricarboxylic acid in 46.2 g of a polyphosphoric aciddehydrating solvent with a P₂ O₅ content of about 76% by weight. Themixture is agitated at 45° C. and atmospheric pressure for about 16hours. The solution is then heated to about 95° C. and 25.0 g of P₂ O₅is added. The reaction continues at atmospheric pressure under anitrogen environment with agitation at 95° C. for about 8 hours, andsubsequently at 150° C. and atmospheric pressure for about 16 hoursgiving rise to a brown/amber solution. A portion of the product isprecipitated in a water bath and repeatedly washed with water to removeresidual solvent. The precipitate is dried to a constant weight in avacuum oven at about 50° C.

The beige/yellow product is believed to be predominately atetra-functional carboxylic acid having the average structure asillustrated in Formula 2. The structure is confirmed by infraredspectrophotometer analysis showing absorption bands associated with thecarboxylic acid and the azole moieties. This tetra-functional carboxylicacid can be used as a branching agent for making branched PBZ polymers.

EXAMPLE 8 Preparation of Branched PBO Polymers Using Tetra-FunctionalBranching Agents

In a nitrogen environment, a solution is formed by loading into a 2liter resin kettle, and thereafter mixing, 115.0 g (0.5398 moles) of4,6-diaminoresorcinol dihydrochloride, 106,72 g (0.5257 moles) ofterephthaloyl chloride, 0.521 g (4.27 mmoles) of benzoic acid, 1.055 g(2.16 mmoles) of the tetra-functional carboxylic acid synthesized inExample 7, and 515.1 g of a polyphosphoric acid dehydrating solvent witha P₂ O₅ content of about 76% by weight. The mixture is agitated with amechanical stirrer at 45° C. and atmospheric pressure for about 16hours. The resulting solution is then heated to about 95° C. and 310.7 gof P₂ O₅ is added. The solution turns a bright yellow and foams ashydrogen chloride gas is released. The reaction continues at 95° C. andatmospheric pressure for 24 hours and subsequently at about 150° C. anda 0.5 mm Hg vacuum for an additional 3 hours. At this point, thecontents of the kettle are transferred to a piston reactor as in Example5 to complete the reaction and spin the resulting dope into fiber.

A portion of the fiber is extracted overnight with water in a Soxhletextractor and then dried at 170° C. and 3.0 mm Hg . The fiber is thendissolved in methanesulfonic acid to obtain a solution of 0.044 g/dL.The inherent viscosity is measured at 25° C. in a Schott-Gerate CT 150bath with an Ubelhobde tube as 14.6 dL/g.

COMPARATIVE EXAMPLE A Preparation of Branched PBO Polymers with LargerAmounts of Branching Agent

Incorporation of an excess amount of branching agent within thepolymerization reaction can lead to production of a non-ductile polymerwhich cannot be formed into a fiber or film. The following comparativesample runs are illustrative.

In a nitrogen environment, a solution is formed by loading into a 100 mlresin kettle, and thereafter mixing, 7.50 g (35.2 mmoles) of4,6-diaminoresorcinol dihydrochloride, 6.44 g (31.7 mmoles) ofterephthaloyl chloride, 0.37 g (1.76 mmoles) of1,3,5-benzenetricarboxylic acid, 0.21 g (1.76 mmoles of benzoic acid and33.5 g of a polyphosphoric acid dehydrating solvent having a P₂ O₅content of about 77% by weight. The resulting solution is reacted as inExample 1, with agitation at 45° C. and atmospheric pressure for about16 hours. The solution is then heated to 95° C., at which time 20.3 g ofP₂ O₅ is added giving a bright yellow, opaque solution and foaming dueto release of hydrogen chloride gas. The solution is, at atmosphericpressure, reacted at 95° C. for about 8 hours, 150° C. for an additional16 hours and finally 190° C. for about 24 hours. The resulting polymerdope appears bright green in color, rubbery and non-fiber forming. Thepolymer is isolated from the dope by coagulation in a water bath withthe extraction and drying steps described in Example 1. The resultingbranched polymer product does not readily dissolve in methanesulfonicacid, thereby suggesting that the polymer is crosslinked.

The procedure is repeated using 120,00 g (0.56 moles) of4,6-diaminoresorcinol dihydrochloride, 114.24 g (0.56 moles) ofterephthaloyl chloride, 0.840 g (4.00 mmoles) of1,3,5-benzene-tricarboxylic acid and 517.5 g of a polyphosphoric aciddehydrating solvent having a P₂ O₅ constant of about 76% by weight.After heating to about 95° C. at atmospheric pressure, 344.2 g of P₂ O₅is added. The resulting solution is then heated to about 150° C. for twohours and the contents of the kettle are transferred to the pistonreactor as in Example 5 to complete polymerization and spin fiber.However, after approximately one hour, the piston could not operatewithin the polymer dope and the dope could not be spun into fibers,suggesting what is believed to be the development of a crosslinkedsystem or an undesirably high molecular weigh polymer. The polymer isisolated from the dope as in Example 1. The resulting polymer is solublein methanesulfonic acid with the inherent viscosity measured as inExample 1 to be 22.1 dL/g.

The comparative runs suggest that the presence of an excess amount ofbranching agent produces a polymer dope unsuitable for spinning intofiber.

What is claimed is:
 1. A process for making a branched polybenzazolepolymer comprising contacting, in the presence of at least onedehydrating solvent and under conditions sufficient to form a branchedpolybenzazole polymer, at least one polybenzazole monomer with at leastone branching agent, the at least one polybenzazole monomer and the atleast one branching agent being present in amounts sufficient to form abranched polybenzazole polymer, each polybenzazole monomer containing atleast two azole-forming moieties and being capable of forming apolybenzazole polymer in a condensation polymerization reaction, the atleast one polybenzazole monomer including a first monomer comprising anaromatic group having randomly attached thereto both an o-amino-basicmoiety and an electron-deficient carbon group, each branching agentcomprising a base structure moiety having bonded thereto at least threeazole-forming moieties, each of which, when reacted with anazole-forming moiety from a polybenzazole monomer, forms an azole ring,the at least one branching agent being present in an amount which willproduce a branched polybenzazole polymer substantially free ofcrosslinking.
 2. The process of claim 1 wherein the at least onepolybenzazole monomer is selected from the group consisting of3-amino-4-hydroxybenzoic acid, 3-hydroxy-4-aminobenzoic acid andmixtures thereof.
 3. The process of claim 1 wherein the at least onepolybenzazole monomer further comprises a mixture of (I) at least onesecond monomer and (II) at least one third monomer, the at least onesecond monomer comprising an intermediate bridging group having bondedthereto two electron-deficient carbon groups and the at least one thirdmonomer comprising an aromatic group having bonded thereto twoo-amino-basic moieties.
 4. The process of claim 3 wherein the at leastone second monomer is selected from the group consisting of terephthalicacid, terephthaloyl chloride, 4,4'-biphenyldicarboxylic acid,4,4'-biphenyldicarbonyl dichloride and mixtures thereof.
 5. The processof claim 3 wherein the at least one third monomer is selected from thegroup consisting of 4,6-diaminoresorcinol, 2,5-diamino-1,4-benzenedioland mixtures thereof.
 6. The process of claim 3 wherein the at least onesecond monomer and the at least one third monomer are present in themixture at no more than about a 10% molar excess of either monomer. 7.The process of claim 1 wherein the at least one branching agent isselected from the group consisting of 1,3,5-benzenetricarboylic acid,1,3,5-benzenetricarbonyl trichloride, and mixtures thereof.
 8. Theprocess of claim wherein the amount of the at least one branching agentis from about 0.05 mole % to about 14 mole % of all reactants prior topolymerization.
 9. The process of claim 8 wherein the amount of the atleast one branching agent is less than about 2 mole %.
 10. The processof claim 1 wherein the dehydrating solvent is selected from the groupconsisting of methanesulfonic acid, methanesulfonic acid with addedphosphorous pentoxide, trifluoromethyl sulfonic acid, polyphosphoricacid and mixtures thereof.
 11. The process of claim 1 wherein theconditions include a temperature of at least about 50° C.
 12. Theprocess of claim 11 wherein the temperature is from about 150° C. toabout 240° C.
 13. The process of claim 1 wherein at least oneterminating agent is admixed with the at least one polybenzazole monomerand the at least one branching agent.
 14. The process of claim 1 whereincontact is conducted for a time sufficient to produce a dope comprisingthe branched polybenzazole polymer in an amount of from about 2.5% toabout 20% by weight of dope.
 15. The process of claim 1 wherein thebranched polybenzazole polymer produced has a measured inherentviscosity of at least about 0.5 dL/g when measured at 25° C. inmethanesulfonic acid.
 16. The process of claim 1 wherein the branchedpolybenzazole polymer produced has a measured inherent viscosity of atleast about 5 dL/g when measured at 25° C. in methanesulfonic acid. 17.The process of claim 1 wherein the branched polybenzazole polymerproduced is selected from the group consisting of branchedpolybenzoxazole, polybenzobisoxazole, polybenzothiazole, andpolybenzobisthiazole polymers.
 18. A branched polybenzazole polymercomprising at least one branching agent base structure moiety having aplurality of polybenzazole polymer branches bonded thereto, the branchedpolybenzazole polymer being obtained by polymerization of at least onepolybenzazole monomer that includes a first monomer comprising anaromatic group having randomly attached thereto both an o-amino-basicmoiety and an electron-deficient carbon group, the polybenzazole polymerbeing substantially free of crosslinking.
 19. The branched polybenzazolepolymer of claim 18 wherein on average at least three polybenzazolepolymer branches are bonded to a branching agent base structure moiety.20. The branched polybenzazole polymer of claim 18 wherein thepolybenzazole polymer branches are selected from the group consisting ofbranched polybenzoxazole, polybenzobisoxazole, bolybenzothiazole, andpolybenzobishthiazole polymers.
 21. An article of manufacture comprisingthe branched polybenzazole polymer of claim
 18. 22. A dope comprising atleast one solvent and the branched polybenzazole polymer of claim 18.